There are applications where it would be useful to detect whether a person is inside or outside a certain (monitored) area (e.g. in a bed). Such applications, for instance, include:
Patients that are or should be immobile are expected to be in the bed. Every out-of-bed event is considered to be a potential emergency (e.g. the patient might have fallen out of the bed) that requires some personnel to check whether everything is ok.
Dementia-affected persons or smaller children might not be able to orientate themselves when going out-of-bed during the night so it might be desirable that some responsible person is informed as soon as this happens.
Children might need light in order to fall asleep. When in bed, the light should be switched off after some time (advantageously, after the child had fallen asleep). When the child leaves the bed the light should be switched on again in order to allow the child to fight its fears, and then the cycle of switching off the light again should be restarted.
The above mentioned first and second applications are often subsumed under “fall and wandering prevention” or similar terms. All these applications have in common that a system should detect when someone was in a bed and then is not in the bed anymore. The applications primarily differ in what happens after the detection.
There are a number of products on the “fall and wandering prevention” market. Examples for such products are:
SafeBed (Emfit Ltd.)
This system works with pressure sensors underneath the mattress. As soon as there is a change in pressure (as a result from e.g. a person leaving the bed) an action such as informing medical personnel is initiated. The problem with this class of system is that:
a) The functionality depends upon a pressure sensor underneath a mattress. Therefore, there is a certain threshold value for pressure changes in order to distinguish relevant from irrelevant events (e.g. leaving the bed vs. moving in bed). This often leads to a minimum weight requirement of the person that shall be monitored.b) As the sensors are in the bed, every bed needs to be equipped with the system.
SecNurse (Optex)
This system consists of a conventional camera with infrared illumination and some processing capabilities in order to detect image changes outside an area that have been defined as containing the bed. The problem with this type of systems is that it is difficult to distinguish relevant from irrelevant events. Any change in picture can lead to initiating the action e.g. pets moving across a room. Also, it is very difficult to find a person being in bed as e.g. blankets cover most parts of a person in this situation. In addition, the system performance depends on the light situation in the room.
In addition, there are several systems that employ motion sensors that monitor an area (e.g. one next to the bed). As soon as the sensor detects motion in the monitored area it initiates some action. The problem with this type of systems is that it is difficult to distinguish relevant from irrelevant events. Any detected motion can lead to initiating the action e.g. pets moving across a room. Also, it is impossible to see a person being in bed as only areas outside the bed can be monitored.
Apart from the “fall and wandering” market, there are other products/concepts that include a “person in bed detection” functionality. For instance, one class of systems aims at detecting breathing movements and/or heart beat of persons lying in bed. Often, these systems use some sort of radar functionality, e.g. at 2.4 GHz. If no breathing or heart beat can be detected, the person is either dead or left the monitored area. The problems of this class of systems are: a) The system uses active radiation that might be undesirable in a clinical environment or by the monitored person. b) “Being dead” or “having left a bed” are quite different causes for an event that could lead to either an underestimation of the severeness of a case or an overestimation, which is both undesirable.